Conventionally, batteries (so-called secondary cells) have been used as a power supply source for an electric car. An example of such batteries is the battery pack discussed in Patent Literature 1 and 2.
Recent years have seen the advent of a system for loaning out a plurality of batteries to users of electric cars. With this system, batteries are loaned out to users of the system, and when a used battery is returned from a user, it is exchanged (swapped) with another battery that has been charged. For this reason, such systems are called a battery swap system.